The present disclosure is generally directed to devices that are encapsulated, and in embodiments contain polythiophenes. More specifically, the present disclosure in embodiments is directed to thin film transistors and similar electronic devices that contain a protective layer of a wax, and for example, polythiophenes, such as those illustrated in the above copending patent applications, including those polythiophenes containing repeating thienylene units having side chains, such as alkyl, which are arranged in a regioregular manner on the polythiophene backbone, and which polythiophenes are, for example, useful as active semiconductive materials for thin film field-effect transistors (FETs).
Recently, there has been reported to, for example, attempt to achieve economical devices, a number of organic electronic devices, such as organic thin film transistors (OTFTs), containing organic materials, such as organic conductors, organic semiconductors and organic dielectric materials on flexible substrates. Unfortunately, the lifetime of a number of organic electronic devices is usually short when the devices are exposed to ambient conditions in view of certain interactions of the organic semiconductor layer with the ambient oxygen, moisture, and light causing degradation and/or doping of the semiconductor materials. Thus, to attempt to achieve long operable lifetime devices, the semiconductor layers in the thin film transistor (TFT) devices should be protected from the environment.
To stabilize the organic devices from environmental moisture, oxygen, and ambient light, the present disclosure envisions an encapsulation material that is hydrophobic, density-packed, and light scattering; a solution coatable or jettable material for fabricating a protecting layer for compatibility, mechanical, and manufacturing cost considerations. A number of materials are known for encapsulation of organic electronic devices, particularly organic thin film transistor, such as silicon oxide, poly(vinyl alcohol) (PVA), poly(vinyl phenol) (PVP), and PMMA have been reported for use as protective encapsulation materials for TFTs. Silicon oxide usually involves vacuum deposition, thus, it is not considered as being suitable with a number of OTFTs (organic thin film transistors) fabricated by solution coating or jet printing processes. PVA and PVP are hydrophilic and over time absorb moisture from the air and degrade TFT performance. PMMA is amorphous and may not effectively block environmental oxygen from entering the devices. For long term OTFT stability, a hydrophobic, oxygen and visible light-blocking protective encapsulation layer is needed.
Semiconductive polymers like certain polythiophenes, which are useful as active semiconductor materials in thin film transistors (TFTs), have been reported. A number of these polymers have some solubility in organic solvents and are thus able to be fabricated as semiconductor channel layers in TFTs by solution processes, such as spin coating, solution casting, dip coating, screen printing, stamp printing, jet printing and the like. Their ability to be fabricated via common solution processes would render their manufacturing simpler and cost effective as compared to the costly conventional photolithographic processes typical of silicon-based devices, such as hydrogenated amorphous silicon TFTs. Moreover, desired are transistors fabricated with polymer materials, such as polythiophenes, referred to as polymer TFTs with excellent mechanical durability and structural flexibility, which may be highly desirable for fabricating flexible TFTs on plastic substrates. Flexible TFTs would enable the design of electronic devices which usually require structural flexibility and mechanical durability characteristics. The use of plastic substrates together with organic or polymer transistor components can transform the traditionally rigid silicon TFT into a mechanically more durable and structurally flexible polymer TFT design. The latter is of particular value to large area devices, such as large area image sensors, electronic paper, and other display media. Also, the selection of polymer TFTs for integrated circuit logic elements for low end microelectronics, such as smart cards, radio frequency identification (RFID) tags, and memory/storage devices, may also greatly enhance their mechanical durability, and thus their useful life span. Nonetheless, many of the semiconductor polythiophenes are not, it is believed, stable when exposed to air as they become oxidatively doped by ambient oxygen, resulting in increased conductivity. The result is larger off-current and thus lower current on/off ratio for the devices fabricated from these materials. Accordingly, with many of these materials, rigorous precautions have to be undertaken during materials processing and device fabrication to exclude environmental oxygen to avoid or minimize oxidative doping. These precautionary measures add to the cost of manufacturing therefore offsetting the appeal of certain polymer TFTs as an economical alternative to amorphous silicon technology, particularly for large area devices. Additionally, the electronic devices need protection from oxygen, as indicated herein, moisture, light, and the like. These and other disadvantages are avoided or minimized in embodiments of the present disclosure, and wherein in embodiments there is selected a wax coating, and which wax can be hydrophobic and with suitable crystalline characteristics, and further which wax can be solution coatable and ink jet printable thereby avoiding/minimizing the limitations of certain inorganic coatings, such as silicon oxide which is applied by vacuum deposition processes.